Maize and sorghum are important crops in South Africa, meeting the dietary needs of
millions of people as well as the needs of the feed industry. Fungi within the Fusarium
graminearum species complex (FGSC) have recently become the subject of importance
locally.
Maize kernels and sorghum grain were collected from the National Cultivar Trial over three
and two seasons respectively. A total of 558 samples comprising of six maize and seven
sorghum cultivars were collected from 34 and 22 localities, respectively. Although different
conventional detection, isolation and identification methods were utilized, very low numbers
of FGSC isolates could be obtained from the grain. Molecular identification was based on
the translation elongation factor-1α (TEF1-α) and the ammonia ligase (URA) genes. F.
boothii and F. graminearum s.s. were identified from maize kernels while F. acaciamearnsii,
F. cortaderiae and F. meridionale where associated with sorghum. Results
indicated host-specificity between members of the FGSC.
Total genomic DNA was extracted from all milled kernel and grain samples and analysed for
the presence or absence of FGSC DNA using TaqMan real-time PCR. F. graminearum s.l.
DNA was detected and quantified in over 47% of the samples. These findings contradict
previous reports that stated that this group of fungi is of minor importance. Reasons may be
improved detection techniques as well as changes in agronomic practices, such as rotation of
maize with wheat in South Africa, or to other shifts in environmental factors.
DON and ZEA concentrations were quantified using CD-ELISA. In the absence of an
ELISA test for NIV, a selected number of samples were used in LC-MS/MS based detection
and DON, NIV and ZEA were quantified. Concentrations varied considerably and no
correlation between the two techniques was found. Based on CD-ELISA, maize and
sorghum contamination with DON and ZEA differed significantly between seasons, localities
and in some instances cultivars. An analysis of variance across all three seasons showed
significant crop by locality interactions. In maize, high levels of DON were detected in the
2007/08 season, in particular at Delmas, while during the same season ZEA contamination of
maize was significantly higher at Bothaville. In sorghum, DON and ZEA contamination was
highest during the 2008/09 season, although both toxins were detected in the preceding season. In both the 2007/08 and 2008/09 seasons, Cedara was the most conducive locality
for grain contamination with both toxins.
Trichothecene chemotyping was conducted using both simplex and multiplex PCR. All the
F. boothii and F. graminearum s.s. isolates from maize were DON/15-acetyldeoxynivalenol
(15-ADON) producers and F. acacia-mearnsii, F. cortaderiae and F. meridionale isolates
from sorghum grain produced NIV. DON can act as a virulence factor in plant disease and is
usually associated with greater pathogenicity on plants than NIV producers. On the other
hand, NIV is believed to be more toxigenic to both humans and animals. Isolates of the 15-
ADON chemotype are reportedly less toxic that those of the 3-ADON chemotype. The 3-
ADON chemotype was not recorded in this study. However, more FGSC isolates need to be
collected from South African cereal grains and evaluated for their mycotoxin potential to
establish safety guidelines for end users of these products.
The results of this study showed that levels of field infection of maize and sorghum grain by
the FGSC are of significance. Future studies need to quantify the relationships between
members of the FGSC and their tricthothecene and ZEA production in South African maize
and sorghum production systems including the role of cultivar choice, weather, rotation,
tillage and other practices with the aim of establishing intervention technologies.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-07182013-095052 |
| Date | 18 July 2013 |
| Creators | Mavhunga, Mudzuli |
| Contributors | Dr SH Koch, Prof BC Flett, Prof NW McLaren |
| Publisher | University of the Free State |
| Source Sets | South African National ETD Portal |
| Language | en-uk |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.uovs.ac.za//theses/available/etd-07182013-095052/restricted/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University Free State or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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